It is known that cellulose fibre can be made by extrusion of a solution of cellulose in a suitable solvent into a coagulating bath. One example of such a process is described in U.S. Pat. No 4,246,221, the contents of which are incorporated herein by way of reference. Cellulose is dissolved in a solvent such as a tertiary amine N-oxide, for example N-methylmorpholine N-oxide. The resulting solution is extruded through a suitable die to produce filaments, which are coagulated, washed in water to remove the solvent and dried. The filaments are generally cut into short lengths at some stage after coagulation to form staple fibre. This process of extrusion and coagulation is referred to as "solvent-spinning", and the cellulose fibre produced thereby is referred to as "solvent-spun" cellulose fibre. It is also known that cellulose fibre can be made by extrusion of a solution of a cellulose derivative into a regenerating and coagulating bath. One example of such a process is the viscose process, in which the cellulose derivative is cellulose xanthate. Both such types of process are examples of wet-spinning processes. Solvent-spinning has a number of advantages over other known processes for the manufacture of cellulose fibre such as the viscose process, for example reduced environmental emissions.
Fibre may exhibit a tendency to fibrillate, particularly when subjected to mechanical stress in the wet state. Fibrillation occurs when fibre structure breaks down in the longitudinal direction so that fine fibrils become partially detached from the fibre, giving a hairy appearance to the fibre and to fabric containing it, for example woven or knitted fabric. Dyed fabric containing fibrillated fibre tends to have a "frosted" appearance, which may be aesthetically undesirable. Such fibrillation is believed to be caused by mechanical abrasion of the fibres during treatment in a wet and swollen state. Wet treatment processes such as dyeing processes inevitably subject fibres to mechanical abrasion. Higher temperatures and longer times of treatment generally tend to produce greater degrees of fibrillation. Solvent-spun cellulose fibre appears to be particularly sensitive to such abrasion and is consequently often found to be more susceptible to fibrillation than other types of cellulose fibre. In particular, cotton has an inherently very low fibrillation tendency.
It has been known for many years to treat cellulose fibre and in particular fabric with a crosslinking agent to improve its crease resistance, as described for example in Kirk-Othmer's Encyclopaedia of Chemical Technology, third edition, Volume 22 (1983), Wiley-Interscience, in an article entitled "Textiles (Finishing)" at pages 769-790, and by H. Petersen in Rev. Prog. Coloration, Vol 17 (1987), pages 7-22. Crosslinking agents may sometimes be referred to by other names, for example crosslinking resins, chemical finishing agents and resin finishing agents. Crosslinking agents are small molecules containing a plurality of functional groups capable of reacting with the hydroxyl groups in cellulose to form crosslinks. One class of crosslinking agents consists of the N-methylol resins, that is to say small molecules containing two or more N-hydroxymethyl or N-alkoxymethyl, in particular N-methoxymethyl, groups. N-methylol resins are generally used in conjunction with acid catalysts chosen to improve crosslinking performance. In a typical process, a solution containing about 5-9% by weight N-methylol resin crosslinking agent and 0.4-3.5% by weight acid catalyst is padded onto dry cellulosic fabric to give 60-100% by weight wet pickup, after which the wetted fabric is dried and heated to cure and fix the crosslinking agent. In general, more than 50%, often 75%, of the crosslinking agent becomes fixed to the cellulose. It is known that crease-resistant finishing treatments embrittle cellulose fibre and fabric with a consequent loss of abrasion resistance, tensile strength and tear strength. A balance must be struck between improvement in crease resistance and reduction in such other mechanical properties. It is also known that such treatments reduce dyeability.
U.S. Pat. No. 4,780,102 describes a process for dyeing a smooth-dry cellulosic fabric which comprises padding the cellulosic fabric with an aqueous finishing solution comprising sufficient concentrations of N-methylol crosslinking agent, acid catalyst and polyethylene glycol (PEG) in order to impart smooth-dry and dye receptivity properties to the fabric; drying and curing the fabric for sufficient time and at sufficient temperature to interact the components of the finish with the fabric; and dyeing the fabric with a cellulose dye. The cellulosic fabric is preferably a cotton fabric. The pad bath typically contains by weight 5-10% crosslinking agent, 0.7-0.8% zinc nitrate hexahydrate and 10-20% PEG. Smooth-dry ratings begin to drop off substantially with PEG molecular weights of 600 or less, and on this basis PEG of molecular weight 600-1450 is preferred depending on the level of smooth-dry performance desired.